trying

app.py

@@ -108,9 +108,9 @@ box = (
     .encode(
         x=alt.X("Agency:N", title=""),
         y=alt.Y("YTD Gross:Q", title="Salary Distribution"),
+        opacity=alt.condition(select_bar,alt.value(1),alt.value(0)),
         color=alt.value("#4C78A8")
-    )
-    .transform_filter(alt.expr.not_(select_bar.empty))   
+    )  
     .properties(width=120, height=800)
 )